VOIP in J2ME

I am currently working on VOIP in J2ME. In the initial research, I got to know about MjSip and MMAPI for Voip but in some forums they state that voip can not be implemented in J2ME. Some have said that they have used upto SIP implementation but cannot proceed further. I want to know whether voip applications can be done in J2ME or not. If we can implement it, what are the other packages I have to use other than MjSip and MMAPI. I am a bit confused, Please help.

"Any fool can write code that a computer can understand. Good programmers write code that humans can understand."
--- Martin Fowler

Not an answer, but unless you are doing this purely for your own fun or education (in which case I would advise to base the project on the Android platform), are you certain that there will be a need and a market for this once it is done? JME (what used to be called J2ME) is going the way of the dodo, and while there are still many phones out there that support it, most folks who have a data plan sufficient to use VoIP are probably going to go for Android or iOS instead of JME.